The present invention relates to a tracer unit particularly suitable for use with measuring machines, comprising a plurality of tracer tools which generate an electric output signal for signalling a position of contact of the tracer tool with a workpiece, said position being signalled, in accordance with the type of tracer tool, either when the tracer tool leaves the position of equilibrium or when it passes through a position of equilibrium.
There are known individual tracer tools, both omnidirectional and bidimensional or unidimensional, i.e., in which the tip of the tracer tool is movable along three, or two, or one axis. For example, the tracer tools described in U.S. Pat. No. 4,023,045 of the same Applicant are electronic omnidirectional tracers of the type in which en electric signal is generated when the tracer leaves the position of equilibrium. Other tracer tools, bidimensional and unidimensional, are known for instance from the U.S. Pat. No. 3,727,119 and from the British patent specification No. 855,676.
When carrying out measurings on outer surfaces or in inner regions where it is possible for the whole column of the machine to be penetrated along its axis (axis z), or when utilizing bidimensional or unidimensional tracers, it is sometimes necessary to use tracer tools whose axis is disposed in successive stages along different directions. Therefore, it is necessary to detach the individual tracer tool from the head of the measuring machine and to substitute it or to dispose it in another position.